The invention relates to an optical display for the rendition of pictorial representations, colour patterns or items of information. The pictorial representations, colour patterns or items of information are rendered by optically exciting fluorescent substances in a transparent or semitransparent shaped plastic article which is provided with means for controlled light output.
Shaped articles made of transparent or semitransparent plastics, which are dyed using fluorescent substances, are known (EP 0 025 136 and EP 0 032 670). They are, for example, used for objects of furniture or decoration. The light is applied flat to such known shaped articles using an external source. The fluorescent light becomes visible at the edges of the shaped articles. The light source used in this case is ambient light from lamps or sunlight. These known shaped articles have no internal structuring or surface structuring and are not used for the rendition of pictorial representations, colour patterns or items of information.
Recently, fluorescent substances have been used to coat blue light-emitting diodes in order, by means of luminescent conversion, to produce white light or light of any other desired colour. Such light-emitting diodes are referred to as LUCOLEDs (Luminescent Conversion LEDs) xe2x80x9cDie weixcex2e LED ist daxe2x80x9d [white LEDs have arrived] Fraunhofer Institut fxc3xcr Angewandte Festkxc3x6rperphysik in elektronik industrie 6, 1997, xe2x80x9cNICHIA CHEMICAL Develops Efficient White LED Lampxe2x80x9d, N. S. Shinbun in Supplement to TECHNICAL NEWSLETTER, 10, Ref. No. 21, 1996). Here again, there is no structuring of the coating containing the fluorescent substances.
The object of the present invention is to use the fluorescent emission from shaped articles made of transparent or semitransparent plastics, which contain fluorescent substances, in combination with the waveguide properties of the shaped articles, in particular for the pictorial representation and rendition of colour patterns or items of information.
The invention relates to an optical display containing one or more shaped articles and a light source. The term shaped articles includes articles configured in any way, for example sheets, plates, ropes, threads, fibres, tubes, spheres, cuboids, cylinders, hollow bodies or rings. The shaped articles consist of one or more transparent or semitransparent plastics. Each plastic contains one or more fluorescent substances. One or more light sources are arranged in such a way that their light is applied to the surface of the shaped article at particular regions of it and propagates through the shaped article. The shaped article contains means for controlled light output, so that the light is output from the shaped article in a controlled way at quite particular regions on the surface of the shaped article.
The light input into the shaped article, usually visible light or UV light, is absorbed through excitation of the fluorescent substances in the shaped article. The fluorescent light emitted by the fluorescent substances has a longer wavelength than the light originally input. The shaped article acts as an optical waveguide for the fluorescent light. Total reflection of a major part of the light takes place at the walls of the shaped article.
Examples of possible means for the scattering of light include structuring in the interior of the shaped article (internal structure), structuring of its surface or a light-scattering layer on particular regions of the surface of the shaped article.
The internal structuring of the shaped article, the structuring of the surface or the coating of the surface with a light-scattering layer, causes scattering of the fluorescent light in the shaped article, so that it no longer strikes the inner walls of the shaped article at the correct angle for total reflection. This causes the scattered light to be output. The regions on the surface of the shaped article where the fluorescent light is radiated are defined by the structuring, that is to say controlled output is involved. Through appropriate structuring, it is possible for the fluorescent light to be radiated, for example, in the form of pictorial figures, characters or patterns.
The shaped article consists of a transparent or semitransparent plastic, such as thermoplastic, elastomer or thermoset, in which the fluorescent substances are incorporated. Examples of particularly suitable transparent plastics include polycarbonates, polyesters, polyacrylates, polystyrenes, polyvinyl polymers, copolymers of styrene and acrylates, polyacrylonitrile, polysulphones, polyether sulphones, cyclic polyolefins and copolymers and cellulose acetates. Further examples of suitable plastics can be found in H. Domininghaus, xe2x80x9cDie Kunststoffe und ihre Eigenschaftenxe2x80x9d [plastics and their properties] 4th edition 1992 VDI Verlag, Dusseldorf and xe2x80x9cEncyclopaedia of Polymer Science and Engineeringxe2x80x9d, 2nd edition J. Wiley and Sons, New York or J. Brandrup, E. H. Immergut, xe2x80x9cPolymer Handbookxe2x80x9d, 3rd edition, J. Wiley and Sons, New York.
According to the invention, suitable fluorescent substances include all low molecular weight, oligomeric and polymeric substances which exhibit photofluorescence. Examples of low molecular weight substances include organic fluorescent and laser dyes such as coumarins, perylenes, phthalocyanines, stilbenes and distilbenes, distyrenes, methines, azomethines, phenanthrenes, rubrene, quinacridones or optical brighteners based on heterocyclic compounds. Photofluorescent metal and transition metal complexes such as aluminium oxinate, europium complexes, boron chelates or gallium chelates may furthermore be used. For example, poly(para-phenylene vinylene) (PPV) and PPP derivatives such as methoxy-ethylhexyl-oxy PPV (MEH-PPV) are suitable as polymeric fluorescent materials. Polymers with fluorescent segments in the main or side chain may also be used. Various fluorescent substances with different absorption and emission spectra may also be contained in a shaped article.
The internal structuring may consist of light-scattering particles such as glass spheres, glass fibres, metal oxides, SiO2 or minerals, which are incorporated in the shaped article. The particles act as scattering centres for the incident fluorescent light and deviate it in such a way that it strikes the surface of the shaped article at a steep angle and does not undergo total reflection but is instead output. The same effect can be obtained from gas inclusions in the shaped article, which form, inside the shaped article, interfaces at which the incident light is scattered. The particles may themselves also contain fluorescent substances.
Structuring of the surface of the shaped article may consist of light-scattering particles which are incorporated in the surface of the shaped article. The particles act as scattering centres on the surface and output the incident light.
The surface may also be structured using grooves and/or holes. With this type of surface structuring, the scattering centres are created on the surface of the shaped article. The edges of grooves formed in the shaped article may be chamfered.
Printing pastesxe2x80x94for example screen printable formulations or blends or dyesxe2x80x94which are applied using known methods, may be used as a light-scattering layer on particular regions of the surface of the shaped article. At points on the surface which are coated in this way, the incident light is not reflected corresponding to the angle of incidence, but is scattered back into the shaped article. It then strikes the opposite surface of the shaped article at angles which do not allow total reflection, and is output there.
At regions on the surface where no light is output, the shaped article may be coated with a reflecting material, for example a metal layer of aluminium, gold or silver or with another layer having a refractive index which permits total reflection. A coating which is nontransparent over its entire surface is also possible. These reflecting layers improve the waveguide properties, at the points which are not structured or scatter light, and increase the strength of the internal radiation field in the shaped article. This leads to increased intensity of the output light.
In order to produce the shaped articles with fluorescent substances, the fluorescent substances are firstly incorporated in the transparent or semitransparent plastics. The incorporation is carried out using known methods, such as compounding or by co-dissolving the fluorescent substances with the polymer material and subsequent evaporation.
The shaped articles are produced from the plastics containing the fluorescent substances using known methods such as, for example injection moulding or extrusion. Sheets can also be produced from solvents by casting or other known coating methods. It is also possible to use laminates made of a substrate and a sheet that contains the fluorescent materials.
It is also possible to apply solutions of fluorescent substances and the plastic to a suitable base by measures such as casting, printing and spraying.
For internal structuring by the incorporation of particles, such as glass spheres or glass fibres, metal oxides, SiO2 or minerals, the conventional methods of providing additives to plastics are used, for example compounding. For internal structuring by glass inclusions, the customary methods which are employed, for example in foam production are resorted to.
For structuring the surface of the shaped articles with light-scattering particles, in a first step the particles are suspended in a solvent, which dissolves the material of the shaped article, and is applied to the surface of the shaped article using mechanical aids or devices such as, for example, a die or a printing machine. In this case, the regions where the particles and the solvent touch the surface swell. The solvent is then allowed to evaporated. To that end, the shaped article may be heated until the solvent has fully evaporated.
The structuring of the surface of the shaped articles may also be carried out by grinding, scratching, scraping, sawing, drilling, graining, stamping, laser abrasion, matrix printing or other mechanical methods which cause local deformation or alteration of the surface. It may also be structured chemically by etching using a solvent.
The optical display may contain a plurality of shaped articles. The individual shaped articles may, for example, be connected together by adhesive bonding or mechanical devices such as mounts, frames or screw fastenings.
In general, light-emitting radiation sources which are suitable for optical excitation of the fluorescent material in the shaped article and therefore stimulate the visible fluorescent emission, are suitable as the light source. Radiation sources whichxe2x80x94unlike sunlightxe2x80x94have a defined emission wavelength, such as lasers or laser diodes, light-emitting diodes (LEDs), UV lamps or electroluminescent radiation sources, are especially suitable. Inorganic LEDs, UV lamps and electroluminescent radiation sources are preferred. If an electroluminescent component is used as the radiation source, it may be an organic or inorganic emitter.
In order to input the light into the shaped article, the light source may be in direct contact with the shaped article. In order to produce direct contact, the light source may be adhesively bonded to the shaped article, fused onto or into it, pressed on or fitted into bores. The light source may also be in indirect contact with the shaped article but illuminate it only in a locally limited way.
It is also possible to use different light sources at the same time, for example LEDs with different emission wavelengths, for photochemical excitation of the fluorescent substances. If, in addition, different fluorescent substances are used, then it is possible through appropriate choice of the illuminating light source, to stimulate the various fluorescent substances selectively or in common and in this way to produce and output visible light of differing wavelength.
The optical display is used for the rendition of pictorial representations, colour patterns or items of information. The structuring for this is carried out in such a way that the surfaces or regions radiating the fluorescent light form patterns, words, numerals, symbols or other signs. Through the use of fluorescent substances with differing emission spectrum, but overlapping absorption spectrum and localizing the various fluorescent substances at different points on the shaped article, it is possible to represent items of information in various colours at the same time using a narrow-band light source, for example for a single LED.
When using a plurality of excitation light sources which differ in terms of their wavelengths in the optical display, and fluorescent substances which vary in terms of their emission spectra, different pictorial representations or items of information with a variety of colours can be presented successively or at the same time.
Possible uses of the optical display according to the invention include display elements or display units of control panels, dashboards or instrument panels of motor vehicles or other means of transport, which are used for visualization and the presentation of information, switchback-illumination or lights in vehicles or on bicycles.
Other possible applications include back-lighting or lighting units or lamps (designer lighting), interior furnishings, pieces of furniture, picture frames, shelves, promotional articles, light rods or light balls, household goods, a children""s toy, desk accessories, ornaments, xe2x80x9cknick-knacksxe2x80x9d or other objects of daily use.
Other possible uses include traffic signs (for example a stop sign), road signs, information displays (such as emergency exit signs), advertising structures, partitions (for example for setting up exhibitions), publicity signs, illustrated charts and warning signs.
If the shaped articles are used as ropes or fibres, they may also be employed as light-guide systems (POFs: polymeric optical fibres).